I have. I would think most players who've been playing a while can id the notes on their basic accordion, especially if that's the one they learned on, at least the guys I've been around can. It seems easy on a C, but anything else seems not as easy to remember. I can remember the D just because I've tuned so many.

Knowing the notes of my accordions was pretty critical when I was learning songs in the 3rd position, it helped with the transposing since it seemed so unnatural to me to play in that position.